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Heat rules in the United Kingdom: no maximum working temperature

What the Health and Safety Executive says about hot weather and outdoor work in Great Britain: no legal maximum temperature, employer duties under health and safety law, the outdoor working page and the heat stress page.

Checked against the sources at the bottom of this page on October 8, 2026. Rules, fees and pay change: the source has the last word.

This page reports what the official source says. It is not legal advice: ask the office named here. It restates pages of the Health and Safety Executive (HSE), the regulator for Great Britain, as read on October 8, 2026. Contains public sector information published by the Health and Safety Executive and licensed under the Open Government Licence v3.0; the wording below is our own summary of those pages. Northern Ireland has its own regulator, the Health and Safety Executive for Northern Ireland, and is not covered by the HSE pages read here. The comparison of every place is on the heat rules overview.

No legal maximum

HSE's first page in its temperature guide says there is no law for a maximum working temperature, or for when it is too hot to work, because every workplace is different. It gives the reason that no meaningful upper limit can be imposed, since in many indoor workplaces high temperatures come from the work itself, as in bakeries or foundries. The same page says employers must still follow health and safety at work law, including keeping the temperature at a comfortable level and providing clean and fresh air. HSE gives numbers only for the cold side: an indoor workplace should normally be at least 16 degrees Celsius, or 13 degrees Celsius if much of the work involves rigorous physical effort. That indoor figure is not an outdoor rule.

What the outdoor working page lists

HSE's page on outdoor working says weather can have a serious effect on workers' health, immediately or over a longer time, and gives skin cancer as the long-term example. For hot environments it lists these actions for employers:

  • reschedule work to cooler times of the day;
  • provide more frequent rest breaks and shading in rest areas;
  • provide free access to cool drinking water;
  • introduce shading in the areas where people work;
  • encourage workers to remove personal protective equipment when resting, to help heat loss;
  • make sure workers can recognise the early symptoms of heat stress.

The page also says too much sunlight can cause sunburn, blistering and skin ageing, and links to separate guidance on sun exposure for outdoor workers. Tree crews are not named on the page. The list is guidance, not a numbered rule with a trigger temperature.

Heat stress and protective clothing

HSE's heat stress page says heat stress happens when the body's way of controlling its internal temperature starts to fail. Air temperature, work rate, humidity and work clothing can all play a part. Its example is someone in protective clothing doing heavy work in hot, humid conditions: sweating is restricted, body heat rises with the work rate, and the body sweats more, which may cause dehydration. The page says the guidance is mainly for workplaces where heat stress is an issue all year, and that it also helps employers in very hot weather.

It lists the symptoms as inability to concentrate, muscle cramps, heat rash, severe thirst (called a late symptom), fainting, heat exhaustion (fatigue, dizziness, nausea, headache, moist skin) and heat stroke (hot dry skin, confusion, convulsions and eventual loss of consciousness). It says employers must assess the risk where heat stress is possible, looking at work rate, working climate, clothing and personal protective equipment, and a worker's age, body type and medical factors. The page also names training, acclimatisation, identifying workers who are more susceptible, and health monitoring where a risk remains after controls.

The managing temperatures page says protective equipment reduces the body's ability to evaporate sweat, and that heavy or awkward equipment may add to body heat. For those situations it lists slower work rates, more frequent rotation out of the environment, longer recovery times, facilities to dry the equipment, scheduling work to cooler times and reviewing the risk assessment. It adds that workers should keep wearing the equipment correctly, and gives undoing fasteners for airflow as the example of what not to do.

Sources